High AR flying wing for soaring - RC Groups
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Dec 03, 2010, 10:45 AM
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High AR flying wing for soaring

I am planning another high aspect ratio wing for soaring.I dont want to cut too much into the width of the wing for the elevons , and would like to avoid drag where they meet the wing at their ends.I thought of adding them on as an extension of the trailing edge,as flat , thin plates a few centimetres wide.Any ideas on what extending the trailing edge with very little thickness does to the performance of an aerofoil would be appreciated.I intend to use a light fin and rudder on a carbon rod extension, turned with fine strings, to combine/mix with the elevons to improve the turn.
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Dec 03, 2010, 11:30 AM
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I'm not sure about the effect on performance of extending the t.e.,but what about "tipperons". One could mount them on carbon rod as a live pivot that attached to the servo much like rds. Would that work? I guess you'd need a lot of differential to avoid tipstalls... Regardless, I'm very interested to see the direction that you head in as I'd like to build something similar.
Dec 03, 2010, 11:42 AM
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miniphase's Avatar
Hi Foufly

The Millenium rigid wing hang glider uses flat elevons which I'm guessing helps with ease of storage when the wing is folded. I've often wondered if there are any advantages to a flat control surface 'tagged on'.....
Dec 03, 2010, 07:58 PM
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Thank you both.I have two good leads already! I had in mind something like kevlar but have not used it before.Would that be the best thin, rigid material?With the extended boom and rudder I am going to have some balancing problems.Here in thailand I have found fine tissue paper that is giving me an excellent smooth surface.Its an exciting project......
Dec 05, 2010, 12:33 AM
soarrich's Avatar
This might work:

Part Number: 8667K111
Dec 05, 2010, 08:49 AM
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thanks.I am looking at carbon sheet on HK s site, but may be too heavy.
Dec 10, 2010, 02:35 AM
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The first version is looking interesting.I have flown it without paper covering and the second flight it found a good thermal, a "neck breaker".I went on to cover it in tissue paper(photo) and took it out to trim it this a.m.It is now faster, not a floater.Then a servo failed and it ended it's flight some way up a power pylon!....yes I did...well I could hardly leave it there?The flying site here in Chiangmai is surrounded by hazards,and close; a junior school, Tv transmitters houses, pylons....The idea seems to be successful; the add on aerolons delightfully easy to do, and the slightly raised tips acting as wash out due to the crescent shape..At least I think so The added, mixed rudder gives very good turning.I will make larger versions at home where I dont have to carry it on a small motorbike! !
Dec 11, 2010, 01:38 AM
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more of the same

A couple more photos after more flying this a.m. and two more good, neck- breaking thermals.Some wind ,which made it wander a bit.I will try a variant with some dyhedral for longitudinal stability.I found that I could get it to turn quite flat using the rudder only, something I will follow up.
Dec 11, 2010, 12:26 PM
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Here's another approach to consider.
Dec 11, 2010, 08:52 PM
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Very Nice DT56! What is that, are plans available???
Dec 12, 2010, 01:40 PM
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Originally Posted by soarsimon
Very Nice DT56! What is that, are plans available???

You may need translation, but the photos pretty well describe the build.
Dec 12, 2010, 10:45 PM
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awesome! Thanks' DT56
Now, if only the "content filter" at work would let me view the website...
Dec 12, 2010, 11:37 PM
soarrich's Avatar
IS there a market in USA for a fuse like DT56's? I was thinking of molding something like that, but it's a lot of effort for 2 or 3 fuses.
Dec 21, 2010, 09:04 AM
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Arthur or Martha?

After two crashes (signal and servo failures) I decided to use this for experiments. If reflex is needed to counteract pitching with a wing (and I needed weight at the rear) why not a rod with a minimal stabiliser and minimal fin (vertical stabiliser)? When is a wing no longer a wing? Except that this uses only elevons, still. The stabiliser has a few(2-4) degrees negative incidence which now allows the elevons to follow the profile of the wing and not act as air brakes – reflexed – and the balance and stability are good. The responses up/down, left/right turn are quite good. I can fly it up and down a small field one meter from the ground with no problem. The glide is very good and turning in thermals easy. A combination of wing fences, washout and the fin make its lateral stability very good and its stall – it stops and parachutes! I try to make my electric gliders cruise on low power (slow speed) as flat as possible to see any thermals they enter. Not always possible with a wing plus cambered, lifting aerofoil; with this mini stabiliser it’s possible. It holds a line in some wind ,has good penetration for its weight ,under 200gms, and looks great in the sky. After twice intending to abandon it, I am now very satisfied; it’s easy to build and an exciting compromise. Does it matter if it doesn’t know whether it’s “Arthur or Martha?”…..Some ideas then…
Why does it go up when the elevons/ aerolons are raised? One would expect it to do the opposite. It’s a stabilised wing still working well on elevons! (Could they be used as flaps to increase lift in thermals?) More pitching movement/ force so then it would need more down stabiliser?!!
I have now had it in a dozen thermals and flown it for up to half an hour on a 360 2S battery without thermals so the drag must be low .It has become a favourite! and very easy to build.
Dec 21, 2010, 01:31 PM
While it seems to be a nice little airplane, according to your impressions, it is no longer what I call a flying wing. To me, a "flying wing" is just that- an aircraft where all of the necessary stability is built into the wing all by itself.
That said, I'm glad you've engineered an efficient and fun flying machine. What is interesting is how, like me, you are gaining insight into the aerodynamics of flying wings by experimenting and drawing conclusions based on the results of your experiments.

Keep on Truckin'!

I came up with a free-flight flying wing design in the early '80's, which I patented and later was marketed by others as "Sling Wing". This all sheet foam little glider is equipped with a spring-loaded hinge at it's center, that allows it to be folded for catapult launching. This allows the glider to be launched to as high as 80', so that it's glide characteristics can be observed over time. I taught myself a lot with them during the early months of it's development.

One thing of note is how the shape of the lift distribution curve affects the lateral handling qualities of swept back flying wings. The efficient elliptical curve, which results from using the aft end of the usable CG range, can result in a "control reversal" phenomenon in regards to aileron input. If the CG is far enough forward to cause the outboard area of the elevon or the entire wing tip to be negatively loaded, then the Lift distribution curve becomes "bell shaped" and good predictable roll control will be experienced.
The problem is that the bell shaped curve is inherently less efficient. You'll get the best L/D by using the elliptical curve.
Please keep in mind here that I'm referring to a "pure" flying wing that has no vertical stabilizers.
Anyway, to cut to the chase here, the elliptical curve will work very well (in regards to roll control) if enough anhedral (negative dihedral) is incorporated into the design. The anhedral must be of sufficient value to at least cancel out the dihedral effect found in swept-aft planforms, which is generally considered to be about 1 degree of dihedral for every 5 degrees of sweep.
Also please keep in mind that I'm referring to a flying wing that is intended to be flown up-right, most, if not all of the time. The flying wings usually being discussed on this forum are mostly intended for high speed aerobatic flight. 99% of my flying wings have been non-powered or only minimally powered gliders.

I adjust my anhedral angle so that the glider exhibits a little bit of negative spiral stability, it wants to roll in to the turn, so that while I'm thermalling I'm having to "high side" the stick. So if I'm in a left hand turn, the glider is holding the desired bank angle with the left elevon down slightly and the right side elevon is raised a bit. This yields a very favorable distribution of both lift and drag forces along the span, resulting in the best sink rate and the smallest turning radius at the lowest speed.
Another thing before I go, is the radius of the airfoils' leading edge. You often hear of folks having trouble with tip-stalling when using swept-back wing planforms. Swept-back wings have in addition to an inherent dihedral a wash-in effect as well. A flying wing intended primarily for up-right thermalling flight needs to have some wash-out built into the wing. Insufficient wash-out, combined with a small leading edge radius, will ensure tip-stalling problems. Another culprit here is excessive taper in the planform. It will be noticed that modern swept-aft flying wing designs have minimal taper and are quite often equipped with a constant-chord wing design. If you want a lot of taper because you're trying to fly a scale model of a Horten design you will want to provide plenty of twist (washout) to avoid tip stalls. If your flying wing seems eager to tip stall or spin, the easiest fix is to add washout or if that isn't practical then adding more "roundness" to the leading edge radius may help.

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